Landa (of the U.S. Geological Survey) reported in 2005 Uranium mill tailings (UMT) are the crushed ore residues from the extraction of uranium (U) from ores. Except where ores have a high-carbonate content, the commercial extraction of U from ores generally involves leaching with sulfuric acid (H2SO4) [Note: Such acid is not used in in situ mining in the U.S., although such acids are used in Australia (Mudd, 2000).]
The effluent (termed raffinate or barren solution) and tailings from the mill are discharged as slurry to a waste-retention pond or to mined-out underground workings for disposal [or to support adit roof structures?]. As the ores typically are low grade, essentially all of the tonnage of ore processed at the mill is disposed of as tailings. [Note: Misinformation here. The ore grade from underground mines are generally fairly high].
The present inventory of UMT in the United States is about 240 million tons. The final product of the milling process is a U concentrate called yellowcake. U extraction efficiencies at commercial mills range from about 65% to 95% (from Mudd, 2000 in Australia). Because solubilization of 226Ra from ore minerals in both sulfuric acid and sodium carbonate is low, the tailings remain a radiological hazard. Safe management of tailings has been the focus of regulatory and environmental research attention since the 1950s.
Among the radioactive wastes associated with the nuclear fuel cycle, UMT are unique in terms of their volume and their limited isolation from the surficial environment. For this latter reason, their management and long-term fate has many interfaces with environmental microbial communities and processes.
Landa concluded that the interactions of microorganisms with UMT have been shown to be diverse and with significant consequences for radionuclide mobility and bioremediation. These radionuclides are associated with the U-decay series. Recent proposals (Kirk, 2004) have called for the use of UMT disposal facilities in the United States for the disposal of other forms of low-level radioactive wastes; such usage has apparently occurred in Germany, where the fission product technetium-99 has been detected at a UMT disposal site (Koss, 1992). Mixed-waste operations such as these may require us to broaden our view of these microbial processes to consideration of other radionuclides.
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